1. Field of the Invention
The present invention relates to an image reading apparatus for reading image information on an object to be read by a scanning operation, and more particularly, it relates to an image reading apparatus having different scanning systems in which, when the object to be read is a book having a substantial thickness, the object is read while shifting an image reading unit, and, when the object to be read is a thin sheet, the object is read while shifting the object and which is applicable to a facsimile system or a copying machine.
2. Related Background Art
Among conventional reading apparatuses in which an image sensor of close contact type consisting of combination of a light emitting element array and a light receiving element array is used as an image reading device, there is an image reading apparatus having a function for reading two-dimensional image information from a thick object to be read such as a book and a function for reading two-dimensional information continuously from a plurality of fixed-shape sheets to be read.
Briefly explaining, when a thick original such as a book is read (first mode), the original is rested on a transparent plate and an image on the original is read while shifting a reading device.
On the other hand, when a sheet-shaped original is read (second mode), the original is rested on a tray, and an image on the original is read while automatically conveying the original onto a transparent plate by means of convey rollers. In this case, the reading device is stopped at a predetermined position in order to read the image on the shifting original.
However, in the second mode, since the sheet-shaped original conveyed while applying a slight tension force to the original along a conveying direction to prevent the slack of the sheet-shaped original at a reading position, the reading is effected in a condition that the sheet-shaped original is not completely contacted with the glass plate. To the contrary, in the first mode, the original is closely contacted with the glass plate.
Accordingly, when a light emitting amount of the light emitting element is constant, illuminance on the original differs between the first mode and the second mode. If the illuminance differs, reading density will be varied even regarding the original having the same image density.
In a facsimile having an automatic original (document) feeder (ADF) and an original support plate, when the original is read from ADF, for example, as shown in FIG. 10, while the original is being read, diffused reflection light and/or stray light (shown by the arrows) from a light source 201 is incident on a light receiving element 203. On the other hand, when the original is read from the original support plate, for example, as shown in FIG. 11, since the original 206 is urged against the original support plate 501 by a pressure plate 502, the diffused reflection light and/or stray light is not incident on the light receiving element 203. Incidentally, in FIG. 11, the reference numeral 301 denotes an image sensor.
In the conventional facsimiles, when image data is accumulated in a memory, output is emitted with low resolving power; whereas, when the image data is not accumulated in the memory, output is emitted with high resolving power. However, in any cases where the image data is outputted with low resolving power and where the image data is outputted with high resolving power, the same luminance/density conversion table is used.
However, in the above-mentioned conventional techniques, when the original conveyed from the ADF is read, since the diffused reflection light and/or stray light is incident on the image sensor, a reading illuminance value becomes greater in comparison with a reading illuminance value when the original is read from the original support plate. Thus, there is a disadvantage that density of an output image is reduced.
Further, in the above-mentioned conventional techniques, when the output resolving power is changed, a recording dot width is also changed. Thus, since gradient of a recording apparatus is varied with the output resolving power, even when the same density value is outputted during the recording, density of images is varied.
The present invention aims to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide an image reading apparatus in which the reading can be effected with high accuracy.
Another object of the present invention is to provide an image reading apparatus in which difference in reading density between a first mode and a second mode is small.
A further object of the present invention is to provide an image reading apparatus comprising a transparent plate, a convey means for conveying an original onto the transparent plate, a light source for illuminating the original, a light receiving element for reading an image of the original illuminated by the light source through the transparent plate, the light receiving element is shifting in a first mode in which the original stopped on the transparent plate is read and being kept stationary in a second mode in which the original is being shifted by the convey means is read, and a control means for controlling a light amount of the light source in accordance with the first mode or the second mode of said light receiving.
A still further object of the present invention is to provide an image reading apparatus comprising a transparent plate, a convey means for conveying an original onto the transparent plate, a light source for illuminating the original, a light receiving element for reading an image of the original illuminated by the light source through the transparent plate, the light receiving element is being shifted in a first mode in which the original stopped on the transparent plate is read and being kept stationary in a second mode in which the original being shifted by the convey means is read, and a conversion means for determining image density in accordance with an output from the light receiving element, which conversion means includes a first conversion table for the first mode and a second conversion table for the second mode.
The other objects of the present invention will be apparent from the following detailed explanation of the invention.